One of the main sources of small engine noise is the hot gases that are forced out of the cylinder during each exhaust stroke. A muffler does a good job of reducing exhaust noise. But after a season or two, exhaust gases leave a layer of soot in the muffler that creates additional resistance to gases exiting the cylinder. When hard soot accumulates, when the exhaust emits excessive noise or when cracks or holes appear, don't try to repair the muffler. Once a muffler shows signs of deterioration, replace it. This section covers the procedures for removing, inspecting and replacing your muffler. It's an inexpensive and simple job if you take the proper precautions. Always wait for the engine to cool completely before handling the muffler. The muffler's surface can remain very hot and can easily cause a burn, even after the engine is stopped. A rusty muffler can cut you, especially if it crumbles during replacement. If any sharp edges are exposed, use slip-joint pliers to remove the muffler.
How Your Muffler Works
The force of exhaust gases as they rush through the small opening in the exhaust valve produces shock waves. It's the muffler's job to reduce noise by routing the exhaust through a series of perforated baffles and plates that break up the sound waves. The inside of the muffler also functions as a spark arrestor, preventing exhaust sparks from exiting and igniting dry grass, leaves or debris.
We quickly notice when a muffler is not doing its job. Even small cracks or holes in the muffler can result in a dramatic increase in engine noise.
Inspecting The Muffler
NOTE: MUFFLER'S SURFACE CAN REMAIN VERY HOT AND CAN EASILY CAUSE A BURN, EVEN AFTER THE ENGINE HAS STOPPED. ALWAYS WAIT FOR THE ENGINE TO COOL COMPLETELY BEFORE HANDLING MUFFLER.
- Locate the muffler, which is usually near the cylinder head.
- To determine if your muffler needs to be replaced, remove the muffler (cold) and shake it; there should be little or no noise heard, and limited amount of rust/debris coming from the inside. If a significant amount of noise and/or debris results from shaking, the muffler has probably deteriorated inside.
- Check the outside of the muffler for signs of rust, dents, holes or cracks, any of which can restrict the exhaust and reduce the effectiveness of the muffler.
Removing The Muffler
The muffler body may be attached directly to the engine with mounting bolts or screwed into the engine body. On some mufflers, an extended pipe threads into the engine.
If the muffler is attached with mounting bolts and has locking tabs around the bolts, bend the tabs back far enough to fit a wrench over the bolt heads. Remove the bolts (image A) and detach the muffler.
If the muffler screws directly into the engine, apply some penetrating oil to the threads (image B) and let the oil work for several minutes. Tip the engine very slightly, if necessary to allow the oil to reach the threads. NOTE: Don't tip the engine sharply. This can cause oil to drain into the carburetor and air cleaner.
Some mufflers are fastened with a threaded lock ring. Loosen it by tapping it counterclockwise with a hammer and pin punch. Then, grasp the muffler with slip-joint pliers and unscrew counterclockwise (image C).
To check for soot, tap the muffler body with a mallet or on a hard surface (image D). If the muffler is damaged or large quantities of soot cannot be dislodged, replace the muffler with original manufacturer's parts. If the muffler is in good condition, reattach it.
Don't over-tighten the new muffler. If a lock ring is used, install it using a hammer and pin punch. NOTE: The smooth side of the lock ring must be against the cylinder in aluminum-block engines. The tooth side must be against the cylinder in cast-iron engines.
- Brush the entire area to clear away dirt and debris. If left on the muffler, dried grass clippings and other debris can catch fire on the hot surface of the muffler.
Removing A Rusty Muffler
A very rusty muffler may collapse or crumble as you twist it with a wrench. There's no harm done as long as you take care not to damage the muffler mounting threads in the engine block or other muffler fittings on the engine. If your muffler screws into the engine, cut the muffler body off with metal snips. Then, grasp the stem, using slip-joint pliers, and unscrew (image E). If the muffler breaks off, leaving a connecting pipe attached to the engine, grasp the pipe with slip-joint pliers and unscrew (image F).
If you wish to perform this replacement yourself, a good source for engine specifications and technical servicing information would be a Briggs & Stratton Repair Manual. The correct Repair Manual for your model engine is often listed in your engine's Illustrated Parts List. The "Service and Storage" section of your Operator's Manual will also inform you of which repair manual your engine requires.
Your best source of information regarding any engine concern would be a Briggs & Stratton Authorized Dealer. Your Briggs & Stratton Authorized Dealer has all the information relating to Briggs & Stratton warranty information, replacement engines, short blocks, parts, pricing, service/repair, specifications, etc.
NOTE: Please read and abide by any applicable Safety Information (PDF) before performing any engine work. This information is not meant to take the place of work performed by a Briggs & Stratton Authorized Dealer. Terms and Conditions apply to all of our information provided on this website. Always be sure to read and understand your engine Operator's Manual.